Empirical surveys about medical futility are scarce relative to its theoretical assumptions. We aimed to evaluate the difference of attitudes between laypeople and physicians towards the issue. A questionnaire survey was designed. Japanese laypeople (via Internet) and physicians with various specialties (via paper-and-pencil questionnaire) were asked about whether they would provide potentially futile treatments for end-of-life patients in vignettes, important factors for judging a certain treatment futile, and threshold of quantitative futility which reflects the numerical probability that an act will produce the desired physiological effect. Also, the physicians were asked about their practical frequency and important reasons for futile treatments. 1134 laypeople and 401 (80%) physicians responded. In all vignettes, the laypeople were more affirmative in providing treatments in question significantly. As the factors for judging futility, medical information and quality of life (QOL) of the patient were rather stressed by the physicians. Treatment wish of the family of the patient and psychological impact on patient side due to the treatment were rather stressed by laypeople. There were wide variations in the threshold of judging quantitative futility in both groups. 88.3% of the physicians had practical experience of providing futile treatment. Important reasons for it were communication problem with patient side and lack of systems regarding futility or foregoing such treatment. Laypeople are more supportive of providing potentially futile treatments than physicians. The difference is explained by the importance of medical information, the patient family’s influence to decision-making and QOL of the patient. The threshold of qualitative futility is suggested to be arbitrary.